This invention relates to a cutting insert intended for chip removing machining, which is delimited by a top side, a bottom side and a number of side surfaces extending therebetween, and which has at least one cutting edge between said top side and a side surface serving as a flank. Grooves which are mutually separated and open upwards, are provided in said top side, in connection with the cutting edge, for feeding cooling liquid in the direction towards the cutting edge.
The practice of cooling not only the cutting inserts of cutting tools, e.g. tools for turning, but also the workpiece being machined by the tool as well as the chip being cut from the workpiece has been known for a long time. A fundamental aim within the technology of today for cutting machining is to enable the use of the highest possible pressure in the cooling liquid and to supply the liquid in the form of one or more jets mainly directed towards the cutting insert and the chip released thereby. The higher the pressure that can be used in the liquid jet, the greater will be the possibility to use the liquid jet not only for pure cooling, but also to obtain a mechanical effect on the chip, more precisely with the purpose of breaking up the chips into as small particles as possible. There are various opinions among those skilled in the art about what, in this context, is to be considered as low and high liquid pressure, respectively. In general. though, the classification would be likely to be made in the following intervals:
low pressure  less than 10 bar,
medium pressure 10-100 bar, and
high pressure greater than 100 bar.
In older cutting tools, cooling was carried out using cooling liquid at low-pressure, whereas somewhat more modem cutting tools have worked with cooling liquid at medium-pressure. In the more recent technology, the use of liquid pressures of hundreds of bars is to be found. For instance, U.S. Pat. No. 5,148,728 forecasts the use of liquid pressures as high as 2,800 bar.
When a cutting insert during, for instance, turning cuts loose a chip from a rotating workpiece, usually of metal, considerable amounts of heat are generated. The actual cutting of the chip takes place in a primary shear zone, which is developed in a peripheral portion of the workpiece and extends obliquely upwards, from the cutting edge of the cutting insert. By virtue of the high temperatures developed, not only in the chip and the workpiece, but also in the cutting insert, the chip separated in the primary shear zone cannot slide away across the top side of the cutting insert without being influenced by both friction and resistance. On the contrary, the very hot chip adheres to the top surface of the cutting insert along a certain contact length during a course of events, which has certain similarities to welding. The contact length can, depending on e.g. the material of the workpiece, vary between tenths of a millimetre to a few millimetres backwards from a shear zone which is near the cutting edge. In doing so, the hot material is strongly adhered in a thin layer, above which the proper cutting of the chip takes place by shearing in a secondary shear zone (frequently designated as the weld zone). Hereafter, a so-called friction zone follows, along which the chip is in forceful frictional contact with the cutting insert before leaving this. In order to facilitate the separation of the chip from the cutting insert, mostly some sort of chip deflector is provided; e.g. in the form of bumps or projections on the top side of the actual cutting insert and/or in the form of specific bodies on the tool, in particular clamps for the retention of the cutting insert.
The modern high-pressure cooling-liquid technology aims at introducing the cooling-liquid jet into the substantially wedge-shaped space provided between the bottom side of the chip and the top side of the cutting insert at the point where the chip is initially separated from the cutting insert. The idea is to form a so called hydraulic wedge between the chip and the top side of the cutting insert, and that said wedge should contribute to xe2x80x9cbreak outxe2x80x9d the chip and, as far as possible, reduce the extent of the contact length of the chip along the cutting insert. A fundamental aim with the introduction of high-pressure cooling liquid between the chip and the cutting insert is, of course, also to cool these as effectively as possible. However, the attempts to improve the cooling and the flow of the chip away from conventional cutting insert carried out hitherto have not been entirely successful.
The present invention aims at obviating the above-mentioned shortcomings of previously known technology and at providing a cutting insert having improved capabilities to more efficiently cool and remove the chips. A primary object of the invention is, therefore, to provide a cutting insert which permits access of high-pressure liquid jets to the area below the zone along which the chip is separated from the cutting insert, at the same time as the chip should be broken out from the top side of the cutting insert as effectively as possible. Another object is to provide a cutting insert that guarantees the intended improvement of the cooling and the removal of chips by means of simple and thereby inexpensive means, more precisely by providing the cutting insert with a new geometric shape.
According to the invention, at least the primary object is attained by the providing a top face of an insert with grooves extending toward the cutting edge, and with upwardly extending chip-deflecting projections 9. At least a portion of each projection is disposed closer to the cutting edge than is an inner end of an adjacent groove. A jet of cooling fluid directed toward the inner ends of the grooves travels between the projections and within the grooves toward the cutting edge.
A cutting insert specially constructed for forming threads is previously known through DE 3 740 814, the said insert having a number of grooves for feeding cooling liquid in the direction towards the cutting edge of the cutting insert in the top side thereof. More precisely, three comparatively wide grooves are recessed in the top side of the cutting insert and arranged to co-operate with a separate clamp having the purpose of holding the cutting insert in the appurtenant seat and, at the same time, serving as a chip deflector. The grooves together with the bottom side of the clamp, therefore, define ducts to which cooling liquid is fed from a central main duct in the frame of the cutting tool. This implies, among other things, that the cooling liquid may not be fed in the form of jets with high pressure. Furthermore, this way of feeding the cooling liquid is limited to only the cutting inserts being held by clamps.